How China's Deadly Coronavirus Spread From A Market In WuhanA deadly virus believed to have originated in China was found in the US this week. NPR global health correspondent Jason Beaubien explains what we know and don't know about the disease — and the likelihood it will continue to spread.

Follow Jason on Twitter @jasonbnpr. More of NPR's reporting on the virus can be found here.

UNIDENTIFIED REPORTER #5: Workers outside of the local hospital in bio suits.

SOFIA: ...Seventeen people have died.

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JAY INSLEE: Good afternoon. I'm Governor Jay Inslee, governor of the state of Washington.

SOFIA: On top of all of that...

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INSLEE: We're here today to give a briefing to the public regarding the novel coronavirus.

SOFIA: ...On Tuesday, officials announced it had shown up here in the United States.

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UNIDENTIFIED REPORTER #6: So that patient is a man in his 30s. He is in the hospital here behind me.

SOFIA: And then later in the week, Chinese authorities closed off the city of Wuhan at the center of the outbreak.

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UNIDENTIFIED REPORTER #7: Wuhan's 11 million people are being told they can't leave.

SOFIA: And more Chinese cities have followed suit.

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UNIDENTIFIED REPORTER #8: Such a massive operation to restrict people moving and spreading the disease. It's unprecedented...

SOFIA: So this episode, we'll tell you what officials are saying about the origins of the virus and what we know about the likelihood that it will continue to spread. I'm Maddie Sofia, and you're listening to SHORT WAVE, the daily science podcast from NPR.

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SOFIA: So we're talking coronavirus. And here to help us do that is NPR reporter Jason Beaubien, who covers global health and development.

Hey, Jason.

JASON BEAUBIEN, BYLINE: Hey, Maddie.

SOFIA: So this thing cropped up about a month ago.

BEAUBIEN: Yeah.

SOFIA: And this past week, China announced more cases. And the number of countries where it's been found outside of China continues to grow. And one big thing we haven't mentioned yet is that this weekend is the busiest holiday travel season in China, one of the largest travel seasons in the world.

BEAUBIEN: Yeah, it's like Thanksgiving and Fourth of July all combined into one. Hundreds of millions of people typically travel for the Lunar New Year, which is January 25th. And this brings up something about the virus. Like, does it spread easily amongst people who are on trains? We don't exactly know. The Chinese government has said it appears to be respiratory, but they haven't been able to confirm that that is exactly the route of transmission at the moment - and how communicable it is, how likely it is if people are sitting next to each other on buses and planes and trains that it could spread.

SOFIA: Right. OK. So let's back up and explain what we do know...

BEAUBIEN: Yeah.

SOFIA: ...Starting with where it started, the city of Wuhan in central China.

BEAUBIEN: Yeah. So all indications are pointing to this wholesale meat market in Wuhan. It's a place where they have live animals that are slaughtered. There's also fish that are sold there, as well as meat. And the idea is that the coronavirus - seems to be what has happened - jumped from one of those animals in the market over to humans.

SOFIA: And at this point, we don't know exactly what animal that is.

BEAUBIEN: We don't. That is one of the big questions that's still out there. If you remember SARS - that big outbreak started in 2002, and it was really big in 2003 - it's called severe acute respiratory syndrome - that was also a coronavirus. And it spread all over the world. Almost 800 people were killed before it was eventually stamped out. And health officials in China say that this current virus doesn't look as deadly as that, but it's still really serious.

MATTHEW FRIEMAN: For SARS, it was these palm civet cats that were being sold in animal markets in China. And once that was identified, then the Chinese government banned the sale of civet cats.

BEAUBIEN: That's Matthew Frieman. He's a virologist at the University of Maryland School of Medicine.

SOFIA: Right. OK. So I want to talk a little bit about how a virus like this can jump from animal to human because it's not often explained super clearly.

BEAUBIEN: Yeah.

SOFIA: So a key part of that jump is when a virus mutates. And when people talk about mutations and viruses, what they're talking about is something that actually happens naturally when a virus replicates, right? So viruses love to make lots of little copies of themselves. And when they do, they can make little mistakes during that. And those can change who or what the virus can infect.

BEAUBIEN: That's right. And Matthew Frieman, that virologist - he thinks that SARS actually started out in bats, and it mutated, and it jumped over to those civet cats. And then it eventually got into people. And here's how he described it.

FRIEMAN: As these viruses replicate in these - in bats, they mutate a bit. And if the wrong bat and then the wrong other animal become in contact potentially when they're caught in the wild, whether they're brought onto farms, then it can jump into that species. And oftentimes, what we found is that the virus needs a little bit more mutational events to happen where it can then replicate in this intermediate animal before it can jump into people.

BEAUBIEN: Right. And there are other types of coronaviruses that exist in birds, in rodents, in camels. But in this case, it's proving difficult to figure out what the exact animal source is of this coronavirus.

SOFIA: Right, which brings us back to that market in Wuhan where they think it all started.

BEAUBIEN: Yeah. We spoke to this guy Kevin Olival who's the VP of research at the public health nonprofit. It's called EcoHealth Alliance. He's been to a lot of markets like this one in Southeast Asia. And he said they can have a wide variety of animals - some of them wild, some of domestic. And it creates a kind of melting pot where it's possible for these viruses to jump between species.

KEVIN OLIVAL: Well, the animals are alive in the market. They're stressed out. There's a lot of contact with feces and saliva - and in terms of butchering the animals - with blood. You know, it's pretty chaotic. It's not as clean as you would think. And there's a lot of contact with animals and animal fluids and body parts.

BEAUBIEN: And so you can imagine in that type of environment...

SOFIA: Yeah, yeah.

BEAUBIEN: ...It's really hard to zero in on one particular animal as a source, you know. In this instance, there's some question about how careful the Chinese government has been in dealing with this. Once they found out that there was this big problem, they went in and cleaned everything up. And some of the researchers are a little bit upset that a lot of potentially useful evidence got destroyed in this effort to just clean up this market.

SOFIA: Right. They kind of reacted quickly, and now it makes it harder to trace that virus.

BEAUBIEN: Yeah. So now the scientists - because they did that cleanup, the scientists are sort of playing catch up. They're sampling animals in other markets to try to see if they have the virus. And in the meantime, there could potentially still be animals spreading this type of virus in other markets in China.

SOFIA: Right, right. And then, of course, beyond that, they're saying it's now spreading not just from animals to humans but from one human to another. Do we have any other clues about that human-to-human spread that's happening?

BEAUBIEN: This is one of the big questions that's still out there.

SOFIA: Yeah.

BEAUBIEN: Like, what is the human-to-human spread? Does it have to be really close contact? Is it spreading through the air? We talked to this epidemiologist at the London School of Hygiene and Tropical Medicine - David Heymann. He says one clue is that there seems to be many clusters of infected people who all belong to the same family and they've had intense contact with an infected person.

DAVID HEYMANN: It doesn't seem that the current virus spreads very easily face to face, like with a cough or sneeze.

BEAUBIEN: But Heymann said we still don't know what share of the infections happened through these family clusters. This case in Washington State, that patient says he didn't visit any of these markets. He doesn't recall coming into contact with anyone who was sick.

SOFIA: Right.

BEAUBIEN: And also, Heymann brings up another thing that's kind of concerning which is that at least 15 health care workers in the city of Wuhan are reportedly among people who've been infected.

HEYMANN: And that's always an evil omen with an emerging infection because health workers see a disease, they think it's a common pneumonia, they're not as careful as they should be in washing their hands or in patient care. And as a result, they then get infected, and then it spreads within the hospital, or it can spread to their families and then into the community. So...

BEAUBIEN: And the concern is that those workers who may not know that they're actually infected with the virus and feel healthy actually are this phenomenon known as superspreaders (ph) - people who end up actually infecting a lot of other people. And we've seen this in the SARS outbreak. There were some superspreaders (ph). There were some key people who ended up spreading the virus to a lot of other people. And that really contributed to the spread of SARS globally. So the question is, are there superspreaders (ph) with this coronavirus? We don't really know that yet.

SOFIA: Gotcha. And in the meantime, when the CDC announced it confirmed that there's that American patient, it also announced screening at certain airports here in the States.

BEAUBIEN: Right. And as we talked about, airports, we should mention, screenings were implemented during the SARS outbreak. They didn't have much of an impact on containing SARS.

SOFIA: Right.

BEAUBIEN: That said, the CDC screening is happening now at airports in LA, San Francisco, New York, Atlanta, Chicago. And basically, if a passenger gets off a plane with a fever or they seem to have cold-like symptoms, they're going to be taken aside for health screening testing. Now, you know, even in the best case, that's going to take hours. These samples are getting sent back to the CDC in Atlanta. So if you're flying from Wuhan, you're going to be routed into one of these airports where they're able to check you and see if you're showing signs of having this disease.

SOFIA: Gotcha, gotcha. OK. So Jason, this is obviously getting a lot of attention...

BEAUBIEN: Yeah, yeah.

SOFIA: ...Right now. What are public health officials and journalists like yourself the most worried about?

BEAUBIEN: Look; the worst case scenario is an airborne flu that spreads rapidly around the world, has maybe a long incubation period, gets out there and then kills lots of people.

SOFIA: Yeah.

BEAUBIEN: That's not really what we're seeing at the moment. But it is still concerning because you are getting spread that we don't know exactly how it's happening. So that's what's most concerning at the moment - that we don't know how it's spreading, and we don't know the underlying number of people who've been infected or how long that incubation period is, which could mean we've got a whole slew of them coming down the pipe.

SOFIA: Sure, sure.

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SOFIA: OK. Jason Beaubien, thank you for the update.

BEAUBIEN: You're welcome.

SOFIA: We'll link to NPR's recent reporting on coronavirus in the notes of this episode, which was produced by Brent Baughman, edited by Andrea Kissack and fact-checked by Emily Vaughn. I'm Maddie Sofia, and we're back next week with more SHORT WAVE from NPR.

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